ETC DEM-ADS82XE

DEM-ADS82xE
®
EVALUATION FIXTURE
FEATURES
DESCRIPTION
● PROVIDES FAST AND EASY
PERFORMANCE TESTING FOR
ADS822/823/824
The DEM-ADS82xE evaluation fixture is designed
for ease of use when evaluating the 10-bit high speed
analog-to-digital converter ADS822, ADS823 and
ADS824. The three converter feature different sampling rates, 40Msps, 60Msps and 70Msps respectively, and each model is available by its individual
demonstration board. Because of its flexible design
the user can evaluate the converter in many different
configurations: either with dc-coupled or ac-coupled
input, single-ended or differential inputs. The data
output of the ADS82x converter are decoupled from
the connector by CMOS octal logic buffers.
● AC- OR DC-COUPLED INPUTS
● SINGLE-ENDED OR DIFFERENTIAL
INPUT CONFIGURATION
● EXTERNAL REFERENCE OPTION
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
© 1998 Burr-Brown Corporation
LI-509
Printed in U.S.A. January, 1998
Transformer Coupled
The demonstration board provides the option to evaluate the
A/D converter with differential signal inputs. Here, a RFtransformer is used to convert the single-ended input signal
applied to SMA connector J3 into a differential signal. The
following steps have to be done to prepare the board:
INITIAL CONFIGURATION
By using solder switches and resistor placements the demonstration board, DEM-ADS82xE, can be set up in a variety of
configurations to accommodate a specific mode of operation. Before starting evaluation, the user should decide on
the configuration and make the appropriate connections or
changes. The demo board comes with following factory set
configuration:
• Remove resistors R19, R20 and R22, R23.
• Remove C41 and replace with a 47pF capacitor.
• OPA681 is set for a non-inverting configuration with a
gain of +2V/V (R9 = R10 = 402Ω). R8, R12, R13, R15, C37
are not assembled.
• Remove R16, C39 (C38).
• Install R18 and R21, typically 22Ω.
• Install RF-transformer (U5). The model TT1-6, for example, is a 1:1 wideband RF-transformer manufactured by
‘Mini-Circuits’. The layout is prepared for the ‘KK81’
case style (surface mount). Note to add a proper termination resistor depending on the selected transformer model.
• With capacitor C39 the output of the driver op amp
OPA681 is ac-coupled to the converter input.
• The converter is set to operate with the internal reference—solder switch JP4 is closed.
• The full-scale input range is set to 2Vp-p. The solder
switch JP3 is open.
• Install R17. Consider to use a 0.1µF capacitor to block the
DC path in the case the input signal carries a DC voltage.
• The required common-mode voltage to bias the input of
the ADS82x is derived from the internal top- and bottom
references by R19 and R20 and applied to the signal input
of the ADS82x, pin 25 (U1).
This differential input configuration can be operated with
external references as well.
CLOCK
The evaluation board DEM-ADS82xE requires an external
clock applied at SMA connector J1. This input represents a
50Ω input to the source. In order to preserve the specified
performance of the ADS82x converter the clock source
should feature a very low jitter. This is particularly important if the converter is to be evaluated in an undersampling
condition.
• The bias for the complementary input of ADS82x is
developed in a similar fashion using R22 and R23.
POWER SUPPLY
The evaluation board typically operates with a ±5V power
supply. This ±5V supply, applied at connector P1, is the
supply for the analog front end and is separated from the
converter supply. The ADS82x is powered with a +5V
supply through connector P2. By using the negative supply
for the driving op amp the applied input signal can be a
ground referenced signal with a bipolar swing and does not
need to be level shifted. However, the input driver, OPA681,
can be set to operate with a single +5V supply as well.
EXTERNAL REFERENCE
The ADS82x converter can be operated with an external
reference. For this solder switch JP4 must be opened disabling the internal references. Close solder switches JP5 and
JP6 and apply the external reference voltage at connector P3.
Refer to the A/D converter data sheet for the recommended
reference voltage ranges.
SIGNAL INPUT
DC-Coupled
The standard configuration of the evaluation board uses the
high-speed op amp OPA681, a current-feedback type op
amp that features low distortion. In order to implement level
shifting for the dc-coupled circuit configuration op amp U4
needs to be re-configured for inverting mode. For this,
remove R9 and install R8. The level shifting voltage is
derived from the +5V supply and applied to the noninverting input. To generate the correct DC-voltage calculate appropriate values for resistors R12 and R13 an close
solder switch JP8. Note that in this configuration the input
impedance to he board is also determined by the input
resistor, R8, and an appropriate termination resistor (R7)
value should be selected.
The selected reference voltage determines the full-scale
input signal range of the converter.
DIGITAL OUTPUT DRIVER SUPPLY, VDRV
The ADS82x converter feature a dedicated supply pin for
the output logic drivers, VDRV, which is not internally
connected to the other supply pins. This allows the ADS82x
to be interfaced to either +3V or +5V logic. On the evaluation board the VDRV supply available at connector P2 is
shorted to the analog +5V supply with the 0Ω resistor, R25.
DATA OUTPUT
The data output is provided at CMOS logic levels. The
ADS82x converter use straight offset binary coding. The
data output pins of the converter are buffered from the I/O
connector, CN1, by two CMOS octal buffer (FCT541).
To change the input full-scale range from 2Vp-p to 1Vp-p
close solder switch JP3.
®
DEM-ADS82xE
2
FIGURE 1. Circuit Schematic DEM-ADS82xE.
3
DEM-ADS82xE
®
AIN
J2
R7
49.9Ω
C4
100µF
+
C3
0.1µF
–5V
3
C37(1)
0.1µF
R12(1)
R11
0Ω
R8(1)
R9
402Ω
2
+5V
1
R10
402Ω
R17(1)
JP8
4
5
+
C31(1)
0.1µF
6
C35(1)
0.1µF
+
+5V
C30
C32(1)
2.2µF –5V 2.2µF
+
C29
0.1µF
3
8
OPA681U
C33
0.1µF
7
2
+
3
(1)
R14
49.9Ω
VDRV
R15
4
3
6
5
TT1-6
2
1
C8
100µF
+
C7
0.1µF
U5(1)
C34 +5V C36(1)
2.2µF
2.2µF
(1)
J3
DIFF. IN
R13(1)
C2
100µF
+
C1
0.1µF
P1
R18
22Ω
(1)
R21
22Ω
(1)
R25
0Ω
2
C39
0.1µF
R16(1)
0Ω
C38
2.2µF
+
(1)
VDD
1
+
C6
100µF
C5
0.1µF
P2
JP5
VDRV
2
JP4
JP3
C24 +
2.2µF
C22 +
2.2µF
VDD
C20 +
2.2µF
C18 +
2.2µF
C16
2.2µF
+
C14 +
2.2µF
1
REFT
VDD
C12 +
2.2µF
C10
2.2µF
C40
47pF
REFT
R24(1)
R19
1.62kΩ
R22
1.62kΩ
R20
1.62kΩ
R23
1.62kΩ
JP6
REFB
REFB
3
C23
0.1µF
28
C21
0.1µF
27
26
25
C41
0.1µF
24
C19
0.1µF
21
C17
0.1µF
22
C15
0.1µF
21
C13
0.1µF
20
C11
0.1µF
19
18
17
16
C9
0.1µF
15
VDRV
VDD
GND
IN
IN
CM
REFT
ByT
ByB
REFB
INT/EXT
RSEL
GND
+VS
OE
PD
CLK
GND
(MSB) B1
B2
B3
B4
B5
B6
B7
B8
B9
(LSB) B10
U1
ADS82xE
1
07
06
05
04
03
02
01
00
D7
D6
D5
D4
D3
D2
D1
D0
OEB
OEA
20
O7
O6
O5
O4
O3
O2
O1
O0
11
12
13
14
15
16
17
18
GND 10
VCC
17
1
3
5
7
9
11
13
15
2
4
6
8
10
12
14
16
18
20
21
22
19
33
23
24
25
26
11
C25
0.1µF
C27
0.1µF
27
28
29
30
31
32
34
35
36
37
38
40
39
12
13
14
15
16
17
18
GND 10
VCC
U2
IDT74FCT541T
D7
D6
D5
D4
D3
D2
D1
D0
OEB
OEA
20
L2(1)
L1
U3
IDT74FCT541T
+5V
VDD
NOTE: (1) Part not assembled.
9
7
6
5
4
3
2
19
1
9
8
7
6
5
4
3
2
19
1
2
R4
10kΩ
R3
10kΩ
R6
10kΩ
R5
10kΩ
VDD
8
JP1
JP2
R1
49.9Ω
3
4
5
6
7
8
9
12
13
14
ADS82xE
EVALUATION FIXTURE
P3(1)
J1 Clock
Input
CN1 OE
CN1 (MSB) B1
CN1 B2
CN1 B3
CN1 B4
CN1 B5
CN1 B6
CN1B7
CN1 B8
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1GND
CN1 GND
CN1 B9
CN1 (LSB) B10
CN1 CLK
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1 GND
CN1GND
CN1 GND
treated like an analog component. Therefore the demo board
has one consistent ground plane. Keep in mind that this
approach may not necessarily yield optimum performance
results when designing the ADS82x into different individual
applications. In any case, thoroughly bypassing the power
supply and reference pins of the converter, as demonstrated
on the evaluation board, is strongly recommended.
PC-BOARD LAYOUT
The DEM-ADS82xE demo board consists of a four layer PC
board. To achieve the highest level of performance surface
mount components are used wherever possible. This reduces
the trace length and minimizes the effects of parasitic capacitance and inductance. The analog-to-digital converter is
FIGURE 2. Top Layer (Component Side) with Silk-Screen.
ORDERING INFORMATION
PRODUCT
ANALOG-TO-DIGITAL CONVERTER
DEM-ADS822E
ADS822E, 10-Bit 40Msps
DEM-ADS823E
ADS823E, 10-Bit 60Msps
DEM-ADS824E
ADS824E, 10-Bit 70Msps
®
DEM-ADS82xE
4
FIGURE 3. Ground Plane.
FIGURE 4. Power Plane.
®
5
DEM-ADS82xE
FIGURE 5. Bottom Layer with Silk-Screen.
COMPONENT LIST
REFERENCE
QTY
COMPONENT
DESCRIPTION
MANUFACTURER
U1
1
ADS82xE
High-Speed ADC, 28-Pin SSOP
Burr-Brown
U2, U3
2
74FCT541
5V Octal Buffer, 20-Pin SOIC
IDT
U4
1
OPA681U
Wideband, Single Op Amp, SO-8
Burr-Brown
R11, 25, L1
3
CRCW0805ZEROF
0Ω, MF 0805 Chip Resistor, 1%
Dale
R1, 7, 14
3
CRCW080549R9F
49.9Ω, MF 0805 Chip Resistor, 1%
Dale
R9, 10
2
CRCW08054020F
402Ω, MF 0805 Chip Resistor, 1%
Dale
R19, 20, 22, 23
4
CRCW08054751F
1.62Ω, MF 0805 Chip Resistor, 1%
Dale
R3, 4, 5, 6
4
CRCW08051002F
10Ω, MF 0805 Chip Resistor, 1%
Dale
R8, 12, 13, 15, 16, 17, 18, 21, 24
9
C2, 4, 6, 8
C10, 12, 14, 16, 18, 20, 22, 24, 30, 34
Open, Use Depends on Configuration
4
ECE-V1CV101SR
100µF/16V, Surface Mount Polar. Alu Cap.
Panasonic (Digi-Key)
10
TAJR225006
2.2µF/10V, 3216 Tantalum Capacitor
AVX
C1, 3, 5, 7, 9, 11, 13, 15, 17, 19,
21, 23, 25, 27, 29, 33, 39, 41
18
08055C104KAT
0.1µF/50V X7R 0805 Ceramic Capacitor
AVX
C40
1
08055C470KAT
47pF/50V NP0 0805 Ceramic Capacitor
AVX
C31, 32, 35, 36, 37, 38
6
Open, Use Depends on Configuration
—
P1, P2
2
ED555/3DS
3-Pin Term Block
On-Shore Technology
CN1
1
IDH-40LP-S3-TG
20 x 2 Dual-Row Shrouded Header
Robinson-Nugent
EF Johnson
J1, J2
2
142-0701-201
Straight SMA PCB Connector
4
1-SJ5003-0-N
Rubber Feet, Black, 0.44 x 0.2
Digi-Key
1
PCB A2403
PC Board A2403, Rev. B
Burr-Brown
®
DEM-ADS82xE
6